Nonequilibrium noise correlations in a point contact of helical edge states

TL;DR

This paper theoretically analyzes the nonequilibrium finite-frequency current noise in a four-terminal quantum point contact of interacting helical edge states, highlighting the effects of scattering processes on fractional charge excitations and noise spectra.

Contribution

It introduces a detailed theoretical framework for understanding how single- and two-particle scattering influence current noise in helical edge states, with implications for topological insulator transport.

Findings

Current noise spectra depend on the Luttinger liquid parameter.

Distinct Fano factors for auto- and cross-correlations compared to quantum Hall edges.

Different regimes dominated by single- or two-particle scattering show unique noise characteristics.

Abstract

We investigate theoretically the nonequilibrium finite-frequency current noise in a four-terminal quantum point contact of interacting helical edge states at a finite bias voltage. Special focus is put on the effects of the single-particle and two-particle scattering between the two helical edge states on the fractional charge quasiparticle excitations shown in the nonequilibrium current noise spectra. Via the Keldysh perturbative approach, we find that the effects of the single-particle and the two-particle scattering processes on the current noise depend sensitively on the Luttinger liquid parameter. Moreover, the Fano factors for the auto- and cross correlations of the currents in the terminals are distinct from the ones for tunneling between the chiral edge states in the quantum Hall liquid. The current noise spectra in the single-particle-scattering-dominated and the two-particle-scattering-dominated regime are shown. Experimental implications of our results on the transport through the helical edges in two-dimensional topological insulators are discussed.